The present invention relates to the liquid phase dimerization of an acrylic compound to form the corresponding dimer. More specifically, this invention relates to the dimerization of acrylic compounds by contacting an acrylic compound with a ruthenium based catalyst in the presence of hydrogen, at a pressure of least about 1 psi and a temperature of at least about 50.degree. C., wherein the catalyst comprises an inorganic oxide catalyst support, trivalent pendant atoms covalently bonded to the support and ruthenium complexed with said trivalent pendant atoms.
It has long been known that the dimerization of acrylic compounds may be catalyzed by ruthenium based catalysts. It is also known in the art that these catalysts may be disposed on a variety of support materials, such as organic polymers and inorganic oxides.
U.S. Pat. No. 3,790,617 to Masada, et al. discloses a process for the dimerization of organic nitriles by contacting them with hydrogen in the presence of a ruthenium catalyst. This catalyst may be prepared by disposing a ruthenium compound, such as RuCl.sub.3, onto a support material, such as active carbon, alumina, silica, diatomaceous earth and pumice. The catalyst may also be promoted by adding promoting compounds, such as an organophosphorus, to the supported catalyst.
U.S. Pat. No. 3,655,724 to Linn, et al. also discloses a process for the dimerization of acrylic compounds by contacting the acrylic compound with hydrogen in the presence of a ruthenium catalyst. This catalyst is prepared by reacting a water soluble ruthenium salt with an aqueous solution of a carboxylic acid to form a ruthenium-acid complex which is absorbed onto a support of charcoal or n-alumina.
Although ruthenium has long been known as a dimerization catalyst, previous processes suffered from the limitation of using catalysts which showed poor stability. These catalysts also often were homogeneous with respect to the reaction mixture, making separation of the catalyst from the reaction mixture difficult and costly.
Recycling of the catalyst is often desirable because the catalyst often accounts for a major portion of the cost of a process. In fact, recycling of the catalyst may be necessary to make a process cost effective. This is particularly true for ruthenium based catalysts due to the relatively high cost of ruthenium metal. In previous processes, however, efficient catalyst recycling is often impractical due to difficulties in separating the catalyst from the reaction mixture. Previous heterogeneous catalysts also suffer from the limitation of readily leaching ruthenium to the reaction medium. This makes catalyst recycling impracticable and increases the process cost over what the cost would most likely be if the catalyst could be recycled.